1. Field of the Invention
The present invention relates to a fuel injection control device.
2. Description of Related Art
JP-A-2008-144749 (US 2008/0228374), JP-A-2009-74535 (US 2009/0056678), or JP-A-2010-223185 (US 2010/0250095) describes a fuel pressure sensor which detects a pressure of fuel downstream of a common rail (pressure accumulating container), and a fuel injection system which detects a variation in fuel pressure generated by a fuel injection as a fuel pressure waveform.
Specifically, a point of inflexion in a start of lowering in the fuel pressure is detected in the fuel pressure waveform, and an actual injection start time is detected based on the time when the point of inflexion appears. A delay period “td” from an injection start time indicated to a fuel injection valve from the actual injection start time is learned. A command signal of the injection start time is set based on the learned delay period “td” in a manner that a target injection start time corresponds to an operation state of an engine with high accuracy.
FIG. 9A is a chart illustrating a variation in injection rate when multi-step-injection is performed in a single combustion cycle. As shown in FIG. 9B, if an interval Tint between injection steps becomes small in a target injection state (the number of injection steps, injection amount and injection start time), the injection steps may be united (integrated) as shown in a dashed line of FIG. 9C. In this case, because combustion state in cylinder becomes different from a predetermined one, gas emission properties may become worse, or output torque variation may be generated.
When the learning of the delay period “td” is in its early state, and when a value of the learning is left as an initial value, actual injection start/end time is deviated from a predetermined value. In this case, actual interval becomes smaller than a required one, and the united injection may be occurred, with high possibility.